0673 — The scheduled time is a message_log column on every message

Context

MessageOptions.ScheduledAt was the schedule producer’s due time, stored inside the row’s options JSON. MessageOptions is what a message requests and a consumer clamps, so the field also appeared in consumer defaults and bounds where it did nothing, Fill and Clamp carried a pass-through note for it, and Equal compared it. The roadmap item asked for the occurrence time to leave the delivery settings and for the storage shape to be chosen: keep the JSON key, or a column.

A first build made the column nullable, NULL on every message no schedule produced. That needed NULLIF on the write and COALESCE on three claim reads, and the zero MessageMeta.ScheduledAt was a trap: no code or lab branched on it, and the playground handler formatted it unguarded.

Decision

• ScheduledAt moves to ProduceOptions. MessageOptions holds delivery settings only; MessageMeta.ScheduledAt is unchanged.
• message_log gains scheduled_at TIMESTAMPTZ NOT NULL: the time the message is for. A schedule’s message carries the due time, a manual Run the moment it ran, and any other produce the moment of the produce unless the producer set the field. Any producer may set it; scheduler-only was a separate decision and stays open.
• The default resolves once at the produce controller beside the idempotency key, so a retried append reuses the same instant. It trails created_at by clock skew between the producer host and Postgres.
• Claims and ListMessages read the column plainly; the JSON key is gone. Pre-v1, the baseline DDL changed in place; both registries stay empty.
• Keeping the JSON key was rejected: the struct that marshals options would still carry the field, so the split would exist on the Go surface only, and every claim scanning options would need a second struct.

Consequences

Rejected 2026-09-06, the same day: the scheduled time is a fact only a schedule’s message carries, and the sparse options document already holds exactly that. A NOT NULL column on every row needed a default that meant nothing. MessageOptions.ScheduledAt and options.scheduled_at stay as they were.

MessageMeta.ScheduledAt is never zero. “This came from a schedule” is the message key, not the time. With a value on every message, the name scheduled_at overstates an ordinary produce; the rename is its own ROADMAP item (the user does not like occurred_at). The delivery consumer attaches no MessageMeta today and is untouched.